In order to have a high functional safety for electronic systems in road vehicles, a standard was set, referred to as Automotive Safety Integrity Level (ASIL).
One basic approach to cover the Functional Safety requirements for sensor Integrated Circuits (IC) is to integrate a periodic diagnostic of the IC. The result of the diagnostic is reported to the system ECU (Electronic Control Unit). In order to allow this diagnostic reporting, a communication channel for diagnostic reporting and/or for diagnostic requests is required.
Most used sensors have only two or three pins, i.e. two or three channels through which the sensor can communicate or is supplied/delivers signals.
In a 3-wire sensor application, an example of the typical pin usage is as follows: one pin for Ground, one pin for Supply and one pin for Sensor Output (often Open-drain output). In known 3-Wire magnetic sensors the sensor output is switched low or high depending on the applied magnetic field (below or above the corresponding threshold).
In a 2-wire sensor application, an example of a typical pin usage is as follows: one pin for Ground and one pin for Supply, where the sensor output signal is send by supply current modulation with two fixed DC current levels. The sensor supply current is switched between two predefined low or high values depending on the applied magnetic field (below or above the corresponding threshold).
In order to cope with the additional communication requirements for diagnostic reporting, some solutions have been suggested.
A first solution is to provide diagnostic reporting on request, using an additional pin. The diagnostic result is reported after receiving a dedicated request (high level) from an additional pin. This nevertheless requires an additional pin leading to package limitations and to a higher cost in manufacturing time and additional components. The main function typically is not available during diagnostic.
A second suggested solution is to combine the main function output signal and diagnostic output signal, by setting, at diagnostic fail, the output in one of both operating states. Nevertheless, this results in a bad separation between the main function output signal and the diagnostic output signal leading to application limitations (e.g. there is no diagnostic if the main function output signal is high). Furthermore, there is a low diagnostic coverage of the open-drain output.
Consequently, there is still need for a good solution for arranging communication for diagnostic reporting in sensor integrated circuits.